Electronic tube apparatus embodying a cavity resonator



Jan. 23, 1951 D. H. SLOAN 2,539,210

ELECTRONIC TUBE APPARATUS EMBODYING A CAVITY RESONATOR Filed Jan. 12, 1946 2 Sheets-Sheet l I 13 '9 Q t 17 a 7 Q L? 25 23 i grz VIVITNESSES: a; INVENTOR W WM David H. Sloan.

ATTOR Jan. 23, 1951 D. H. SLOAN 2,539,210

ELECTRONIC TUBE APPARATUS EMBODYING A CAVITY RESONATOR Filb'd Jan. 12, 1946 2 Sheets-Sheet 2 03 W I \g r & F 23 25' (L9 WITNESSES: I VENTOR g David H Sloan.

ATTORNE is required as in television. multiplied by 21r is known as the Q of the reso- Patented Jan. 23, 1951 UNITED STATES PATENT OFFICE ELECTRONIC TUBE APPARATUS EIMBODY- ING A CAVITY RESONATOR David H. Sloan, Silver Spring, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 12, 1946, Serial No. 640,828

4 Claims. 1

This invention relates to an electronic tube and has particular relation to a tube in which an electron beam is to be established and the capacity across at least a portion of the space through which the beam projects is to form a principal element in a resonant circuit.

In many high-frequenc electronic tubes in which the capacity across a part of the electron beam path is a principal element in a resonant circuit and particularly in tubes embodying a cavity resonator, the ratio of the energy stored to the energy dissipated in' the resonator or resonant circuit per cycle is too high for certain applications such as where a broad frequency band This ratio when nator or resonant circuit.

It is accordingly an object of my invention to provide a new and improved electronic tube apparatus adapted to have the capacity across at least a part of the electron beam path incorporated as a principal element in a resonant circuit.

A further object of my invention is to provide a new and improved electronic tube apparatus embodying a cavity resonator with an electron beam projected therethrough.

Another object of my invention is to provide a new and improved electronic tube apparatus adapted to have the capacity across at least a part of the electron beam path incorporated as a principal element in a resonant circuit, in which the Q of the resonant circuit is substantially reduced.

A still further object of my invention is to provide a new and improved electronic tube apparatus embodying a cavity resonator with an electronic beam projected therethrough, in which the Q of the resonator for the size and shape thereof is substantially reduced.

In accordance with my invention electronic tube apparatus of the type described is provided in which the Q of the resonant circuit is substantially reduced by a focusing of the electron beam between the anode and cathode of the tube to provide a substantially smaller effective crosssectional area of the beam within the tube than at a point immediately adjacent the cathode or other source of the beam. This is accomplished without reducing the total plate or anode current.

The features of my invention which I consider novel are set forth with more particularity in the accompanying claims. The invention itself, however, together with additional objects and advantages thereof may be better understood from the following description of a specific embodiment when read in connection with the accompanying drawings, in which:

Figure 1 is a cross-sectional view of an electronic tube embodying my invention;

Fig. 2 is a partial cross-sectional view taken along the line IIII of Fig. 1; and

Fig. 3 is an enlarged view showing the elements about the electron path in the tube of Fig. 1.

A tube of the resnatron type which embodies a cavit resonator through which an electron beam is projected is shown in the drawings and in a general way is similar to other tubes of this type disclosed in my copending applications, Serial Nos. 526,882, now U. S. Patent No. 2,459,593, granted January 18, 1949; 526,883, now U. S. Patent No. 2,451,987, granted October 19, 1948 and 533,257, now U. S. Patent No. 2,487,078,

granted November 8, 1949, the first two of which were filed March 17, 1944, and the other on March 17, 1945.

. The tube includes a first cavity resonator 5, hereinafter referred to as the anode resonator, which is formed of a first hollow cylinder 1' with a second hollow cylinder 9 of a smaller diameter mounted coaxially therein and extending from a bottom plate ll of the first cylinder 7 through an opening [3 in the top plate l5 of the first cylinder 1. A second cavity resonator El, hereinafter referred to as the cathode resonator, has a portion thereof projecting coaxially into the second cylinder 9. A cathode unit i9 is mounted on a stem 21 within the cathode resonator H and is made up of a plurality of filament wires formed into a generally cylindrically shaped cage-like structure positioned coaxially with respect to the anode resonator 5 at about midway between the top and bottom plates I 5 and H thereof.

An annular anode 23 is mounted within the anode resonator 5 on the outer wall thereof radially opposite the cathode unit E9. The walls of the cathode resonator l1 and the anode resonator 5 in the region between the cathode unit 19 and the anode 23 have a longitudinal slot therein aligned with each filament wire of the cathode unit permitting electrons to pass from the cathode unit to the anode. These slotted walls in the region between the cathode unit and the anode are adapted to function a a control grid and an accelerating grid, respectively, which grids have reference numbers 25 and 27 applied thereto.

A direct current voltage is impressed between the anode 23 and the cathode unit 19 and between the accelerating grid 21 and cathode unit l9 by means of a suitable direct current voltage source 29 connected to the grounded anode 23 and accelerating grid 2'5 and through suitable leads in the stem 2| to the cathode unit 59. The cathode unit l9 is also connected to the control grid 2'5 through a resistor 3i so that during operation .of the tube the control grid 25 is negative with respect to the cathode unit l9. Filament current is supplied to the cathode unit I9 from a suitable current source 33 through leads within the stem 23.

The cathode resonator 1'! extends below the anode resonator and is arranged to receive an electromagnetic energy input through a glass member 35 in the lower wall of the resonator from a suitable transmission line, such as a coaxial conductor or a hollow wave guide mounted at the bottom of the tube. The input energy together with the direct current voltage fields produce an electron beam which is projected from the cathode unit i9 through the interior of the anode resonator 5 to the anode 23, the field in said anode resonator being arranged so that there is a transfer of energy between the electrons and the electromagnetic field within the anode resonator during the travel period of the electrons. Output electromagnetic energy from the anode resonator 5 passes through the annular space remaining in the opening 53 between the second cylinder and the top plate i5. Upon passing through this annular space, the output energy enters an annular region above the anode resonator 5 surrounding a cylinder 37 which may enclose a suitable getter. This output energy is to be transferred to another suitable transmission line, such as a hollow wave guide through another glass member 39 forming part of the wall of the annular region.

It may be noted that suitable conduits for cooling fluid are provided to enable cooling of the upper end of the tube, the anode, the control and accelerating grids, the lower end of the cathode resonator and the stem on which the cathode unit is mounted.

As shown in Fig. 3, each filament wire of the cathode unit is is provided with a concave electron emitting surface facing the anode 23. In addition, the control grid 25 and the accelerating grid 2? as well, are curved to conform with the concave electron emitting surface. As a result of the concave electron emitting surface of the cathode unit and the direct current voltage fields established between the curved grids and the cathode unit, the electron beam is focused so that the effective cross-sectional area thereof within the anode resonator is appreciably smaller than that at a point immediately adjacent the cathode unit.

Now as previously indicated, the Q of a cavity resonator and therefore the Q of the anode resonator in l is equal to the ratio of the energy stored to the energy dissipated in the resonator. This may be written as follows:

Where a; is 211' times the frequency, c is the total capacity across the interaction space within the anode resonator, 71 is the eihciency, V is the direct current plate voltage, I is the plate current and E is the peak high frequency voltage. Since the plate voltage V for proper operation is substantially equal to the high frequency voltage E, the above equation may be rewritten as It is now apparent that if it is desired to reduce the value of Q for a given resonator, it is necessary either to increase the current I or to decrease the voltage V or the capacity 0. However, there is a practical limit below which the voltage V cannot be reduced. This limit is determined by various things including the travel time of the electrons, It is also known that the available current I is limited by the nature of the cathode, and there is a definite ratio of current to capacity for known cathode materials which is too small in any case to enable a reduction in the value of Q to a sufhcient extent for many applications of the resonator.

But the capacity 0 is proportional to the effective cross-sectional area of the electron beam Within the resonator which here may be considered proportional to the cross-sectional area of the beam immediately adjacent the anode. By reducing the cross-sectional area of the electron beam at a point immediately adjacent the anode to a value smaller than that at a point immediately adjacent the cathode, the capacity 0 may be substantially reduced without reducing the total plate current and thereby effect a reduction in the Q of the resonator.

Although a specific arrangement has been de scribed to accomplish focusin of the electron beam to reduce the capacity of the tube and thereby the Q of the resonant circuit, other suitable focusing arrangements may be satisfactorily employed. Moreover, while the reduction of the Q by use of the focusing arrangement is particularly useful and adaptable where the tube embodies a cavity resonator, it is apparent that it may also be employed in other electronic tubes in which at least a part of the capacity across the electron beam path is incorporated as a principal element in a resonant circuit.

While I have shown and described specific apparatus embodying my invention, I am aware that many modifications thereof may be made without departing from the spirit of the invention. I do not intend therefore to limit my invention to the specific embodiment disclosed herein.

I claim as my invention:

1. High frequency electronic tube apparatus comprising a resonator, a tube having an anode and a cathode and means for projecting an electron beam between said anode and cathode the capacity across at least a portion of the space between the anode and cathode being included as a principal element of said resonator and said means including means for focusing the electron beam to provide a smaller effective cross-sectional beam area in said portion than the area or the beam emitted immediately adjacent said cathode and thereby reduce the Q of said resonatcr.

2. An electric discharge device comprising a cathode formed of a cylindrical array of wires each bent into a concave are, an anode cooperative with said cathode and at least one cylindrical section coaxial with said array having slots therein aligned with the wires of said array and having its surface curved substantially parallel to the wires of said array.

3. An electric discharge device comprisin a cathode formed of a cylindrical array of wires 5 6 each bent into a concave arc, an anode coop- REFERENCES CITED native with Sam cathode and plurality of The following references are of record in the cylindrical sections each coaxial with said array and each having slots therein aligned with the wires of said array and having its surface 5 l e of this patent:

UNITED STATES PATENTS curved substantially parallel to the wires of said Number Name Dat array. 2,064,469 Haeff Dec. 15, 1936 4. An electric discharge device comprising a 2,151,765 Hollmann Mar. 28.1939 cathode formed of a cylindrical array of wires 3352591590 n en t al oct, 21, 1941 each bent into a concave arc a viewed from the 10 2, ,8 Llewellyn p 1 2 direction toward which the electrons are emit- "2,306,875 Fremlin 1 Dec. 29, 1942 ted, a cylindrical anode encircling said cathode 2,351,744 Chevigny June 20, 1944 and a, cylindrical cavity resonator connected to 2,400,753 Haefi May 21, 1946 said anode, said cavity resonator being coaxial with said anode and enclosing the path of the i5 electron stream between said anode and cathode.

DAVID H. SLOAN. 

